Method of printing label on optical disk, optical disk unit, and optical disk

ABSTRACT

A visible light characteristic changing layer formed from photosensitive or heat-sensitive material is formed in a location which can be viewed from a part of a label surface of an optical disk. The optical disk is set on a turntable of an optical disk unit while the label surface of the optical disk is directed downward. The optical disk and an optical pickup are moved mutually along the plane of the optical disk. In synchronism with the relative movement, the power of a laser beam output from the optical pickup is modulated in accordance with image data, such as characters or graphic images to be printed, and the laser beam is emitted onto the visible light characteristic changing layer. As a result of the visible light characteristic changing layer being exposed to the laser beam, a visible-light reflectivity of the visible light characteristic changing layer is changed, thereby forming a image corresponding to the image data on the label surface.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method of printing a labelprovided on an optical disk, to an optical disk unit, and relates to anoptical disk in which a label can be subjected to printing byutilization of a laser beam output from an optical disk unit.

[0002] In a recordable optical disk, information about contents recordedthereon (e.g., titles) is described on an optical disk by a user so thatthe recorded contents can be checked visually. In the case of asingle-sided optical disk which is handled as a single disk withoutbeing housed in a cartridge, such as a CD-system optical disk i.e., aCD-R (CD recordable), a CD-RW (CD rewritable), etc. the information isusually written directly on a label surface of the optical disk with apen. According to another method, information about recorded contentsrecorded are edited on a personal computer, and the contents are printedon a label with a printer. The label is then pasted to the labelsurface.

[0003] According to the method in which contents are written directly onthe label surface of the disk, a recording layer is often damaged by astrong writing action effected by use of a stiff pencil. According tothe method of printing a label with a printer, there is a necessity forusing a printer.

SUMMARY OF THE INVENTION

[0004] The present invention has been conceived in light of theforegoing problem and aims at providing a method of forming an image ona label surface of an optical disk, an optical disk unit, and an opticaldisk, wherein an image is formed on a label surface of an optical diskby utilization of a laser beam output from an optical disk unit, therebyobviating a necessity for writing of an image performed with a pen orprinting an image with a printer.

[0005] The present invention provides a method of forming an image on alabel surface of an optical disk, the method comprising the steps of:forming a visible light characteristic changing layer in a positionwhich can be viewed from a label surface side of an optical disk, thelayer changing a characteristic of visible light having entered from thelabel surface side by exposure to a laser beam used for recording asignal and emitted from the part of the label surface; setting theoptical disk on a turntable of an optical disk unit such that a labelsurface of the optical disk is oriented toward a direction in which alaser beam emitted from an optical pickup is to enter; relatively movingthe optical disk and the laser beam along a plane of the optical disk;and modulating the laser beam, in synchronism with the mutual movement,into a specific characteristic in accordance with image data to beprinted, such as characters or graphic images, and emitting themodulated laser beam onto the visible light characteristic changinglayer from the part of the label surface, wherein a reflectioncharacteristic of the visible light having entered the visible lightcharacteristic changing layer is changed by means of exposure, therebyprinting a corresponding image on the label surface. According to thelabel surface image formation method, a laser beam output from theoptical disk unit can be emitted onto the visible light characteristicchanging layer formed in an area which can be viewed from the part of alabel surface of an optical disk, thereby changing the reflectivity,permeability, or light-scattering characteristic of the visible light.In this way, corresponding images, such as characters or graphic images,can be formed on the label surface, thereby obviating a necessity ofwriting images with a pen or printing images with a printer.

[0006] Under the method according to the present invention, the laserbeam used for recording a signal can be a laser beam of predeterminedpower or higher. The optical pickup can be moved in a radial directionof the optical disk while the optical disk is being rotated. The opticaldisk can be made stationary, and the optical pickup is moved in a radialdirection of the optical disk as well as in a direction which isorthogonal to the radial direction of the optical disk and is tangent toa track.

[0007] The present invention also provides an optical disk unitcomprising: a relative movement mechanism for relatively moving anoptical disk set on a turntable while a label surface is oriented in adirection in which a laser beam is to enter, and a laser beam emittedfrom an optical pickup along a plane of the optical disk; a lasermodulation circuit for modulating a laser beam emitted from the opticalpickup; and a circuit for controlling the relative movement mechanismand the laser modulation circuit wherein the control circuit performscontrol operation so as to form an image on a visible lightcharacteristic changing layer by controlling the relative movementmechanism to relatively move the optical disk and the laser beam andcontrolling the laser modulation circuit in accordance with image data,such as characters or graphic images, to be formed on a label surface ofthe optical disk, thereby modulating a laser bean output from theoptical pickup on the basis of the image data, and thereby forming animage corresponding to the image data on the visible lightcharacteristic changing layer, a characteristic of reflectivity,permeability or light scattering of the visible light is changed by theexposure of the laser beam, which can be viewed from the part of a labelsurface of the optical disk. The optical disk unit enablesimplementation of the label surface image formation method according tothe present invention.

[0008] Preferably, the relative movement mechanism includes a rotarydrive device for rotationally driving a turntable and a radial-directionfeed drive device for moving the optical pickup in a radial direction ofthe optical disk; wherein the control circuit can control the rotarydrive device and the radial-direction feed drive device, therebycontrolling relative movement between the optical disk and the laserbeam. In this case, the control circuit can drive the rotary drivedevice to a constant rotating speed, thereby driving theradial-direction feed drive device by a predetermined amount at eachpredetermined rotary position. Further, the optical disk unit canfurther comprise a circumferential-direction position sensor fordetecting a circumferential position on the optical disk, and aradial-direction position sensor for detecting a radial position of theoptical pickup on the optical disk; wherein the control circuit canperform a control operation for modulating a laser beam emitted from theoptical pickup, in accordance with the position detected by thecircumferential-direction position sensor and the radial-directionposition sensor and with image data to be formed on a label surface ofthe optical disk, such as characters or graphic images. The positionalinformation about image data can be expressed as coordinate dataconsisting of a combination of a circumferential position on an opticaldisk and a radial position on an optical disk. Thecircumferential-direction position sensor can comprise a frequencygenerator which is rotated by the rotary drive device to generate asignal of frequency corresponding to rotation, and a multiplier formultiplying the frequency of a signal generated by the frequencygenerator. The relative movement mechanism can comprise aradial-direction feed drive device for moving the optical pickup in aradial direction of the optical disk, and a track-tangential-directionfeed drive device for moving the optical pickup in a direction which isperpendicular to the radial direction of movement and is tangent to atrack of the optical disk; wherein the control circuit can controlrelative movement between the optical disk and the laser beam bycontrolling the radial-direction position censor and thetrack-tangential-direction feed drive device while the turntable is leftin a stationary state. The optical disk unit further comprises acircumferential-direction position sensor for detecting acircumferential position on the optical disk, and atrack-tangential-direction position sensor for detecting a positionwhich is orthogonal to the radial direction of movement and is tangentto a track of the optical disk; wherein the laser beam emitted from theoptical pickup can be controlled in accordance with the positiondetected by the circumferential-direction position sensor and thetrack-tangential-direction position sensor and with image data to beformed on a label surface of the optical disk, such as characters orgraphic images. The positional information about image data can beexpressed as coordinate data consisting of a combination of a radialposition on an optical disk and a position along a direction which isperpendicular to the radial direction of movement of the optical diskand is tangent to a track of the optical disk. Further, the controlcircuit performs relative movement between the optical disk and thelaser beam by turning off a tracking servo and turning on/off a focusservo. The control circuit can perform a control operation for vibratingand driving a tracking actuator of the optical pickup while performingrelative movement between the optical disk and the laser beam. Theoptical disk unit according to the present invention can be embodied in,for example, an optical disk unit for a single-side CD-type opticaldisk, such as a CD-R (CD-R recordable) and CD-RW (CD rewritable); or anoptical disk recording device for an optical disk formed by laminatingtwo substrates; for example, a DVD-type optical disk such as a DVD-R(DVD recordable) or DVD-RW (DVD rewritable).

[0009] The present invention also provides an optical disk comprising avisible light characteristic changing layer which changes a visiblecharacteristic of a visible light by exposure to a laser beam havingentered from a label surfaces and which is formed in a location capableof being viewed from the part of the label surface. The optical diskenables implementation of the label surface image formation methodaccording to the present invention. Since the visible lightcharacteristic changing layer is formed integrally on an optical disk,occurrence of vibration caused by mass eccentricity during high-speedrotation, and occurrence of failure caused by exfoliation of a labelwithin a drive can be prevented, as compared with a label pastingmethod.

[0010] Preferably, the visible light characteristic changing layer canbe embodied in a color-changing layer which undergoes fading, coloring,or changes in color or hue by exposure to the laser beam. Further, thecolor-changing layer can be embodied in a photosensitive or heatsensitive layer, or two layers construction. In case of the two layersconstruction, the two layers are fused or mixed together by exposure tothe laser beam, thereby changing a visible-light characteristic. Theoptical disk can be constituted by sequentially forming, on a substrate,at least a recording layer, a reflection layer, and a protective layer;and the visible light characteristic changing layer can be formedbetween the reflection layer and the protective layer. An intermediatelayer can be disposed between the reflection layer and the visible lightcharacteristic changing layer, in order to improve, for example,adhesion between a reflection layer and a visible light characteristicchanging layer, and to effect insulation control for the purpose ofcontrolling heat conductivity contributing to changes in acharacteristic of visible light or protecting data recorded on arecording surface of an optical disk, the reflection layer and theintermediate layer can be joined directly together, and the intermediatelayer and the visible light characteristic changing layer can be joineddirectly together. The interface between the reflection layer and theprotective layer can be formed so as to be a fine mixture of a partcontaining the visible light characteristic changing layer and a partwhich does not include the visible light characteristic changing layerand is joined directly to the reflection layer and to the protectivelayer. Since the optical disk has a part where the reflection layer andthe protective layer are joined directly together, adhesion can beimproved and there can be realized control of thermal conductivityattributable to change in a visible light characteristic. Even when thevisible light characteristic changing layer is translucence, thereflection layer can be partially viewed from the label surface side viathe part where no visible light characteristic changing layer is presentand the reflection layer and the protective layer are joined togetherdirectly. Focus can be readily achieved on the reflection layer at thetime of formation of an image on the label surface. The structure inwhich there are finely mixed together a part containing the visiblelight characteristic changing layer and a part which does not includethe visible light characteristic changing layer and is joined directlyto the reflection layer and to the protective layer can be embodied in astructure in which the visible light characteristic changing layer isformed between the reflection layer and the protective layer in the formof a plurality of dots or a plurality of voids. The visible lightcharacteristic changing layer can be constituted in the form ofconcentric fringes or linear stripes, rather than in the form of dots orvoids. The optical disk according to the present invention can beembodied in, for example, an optical disk unit for a single-side CD-typeoptical disk, such as a CD-R (CD-R recordable) or CD-RW (CD rewritable);or an optical disk recording device for an optical disk formed bylaminating two substrates; for example, a DVD-type optical disk such asa DVD-R (DVD recordable) or DVD-RW (DVD rewritable).

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a partial cross section showing an embodiment of anoptical disk according to the present invention;

[0012]FIG. 2 is a partial cross section showing a modification of theoptical disk shown in FIG. 1;

[0013]FIG. 3 is a partial cross section showing another modification ofthe optical disk shown in FIG. 1;

[0014]FIG. 4 is a partial cross section showing yet another modificationof the optical disk shown in FIG. 1;

[0015]FIG. 5 is a partial cross section showing another embodiment ofthe optical disk according to the present invention;

[0016]FIG. 6 is a system configuration block diagram showing anembodiment of an optical disk unit according to the present invention;

[0017]FIG. 7 is a plan view showing the locus of movement of a laserbeam on a label surface stemming from an operation for subjecting thelabel surface to printing through use of a CD-R/RW drive shown in FIG.6;

[0018]FIG. 8 is a timing chart showing changes in laser power whicharise during the course of the printing operation shown in FIG. 7;

[0019]FIG. 9 is a plan view showing the locus of movement of a laserbeam over a label surface arising when printing is effected withoutvibrating the laser beam in a radial direction of the optical disk;

[0020]FIG. 10 is a plan view showing the locus of movement of a laserbeam over a label surface arising when printing is performed whilevibrating the laser beam in a radial direction of the optical disk;

[0021]FIGS. 11A and 11B are a plan view and an enlarged partial planview showing an example of a print made on the label surface by means ofthe CD-R/RW drive shown in FIG. 6;

[0022]FIGS. 12A to 12C are plans view showing another example of a printmade on the label surface by means of the CD-R/RW drive shown in FIG. 6;

[0023]FIG. 13 is a system configuration block diagram showing anotherembodiment of the optical disk unit according to the present invention;

[0024]FIGS. 14A and 14B are plan and front views showing an examplelayout of the CD-R/RW drive feed mechanism shown in FIG. 13;

[0025]FIGS. 15A and 15B are plan and front views showing the examplelayout of the CD-R/RW drive feed mechanism shown in FIG. 13;

[0026]FIG. 16 is a plan view showing an example of a print productformed on the label surface by means of the CD-R/RW drive shown in FIG.13.

[0027]FIG. 17 is a partial cross section showing another modification ofthe optical disk shown in FIG. 1;

[0028]FIG. 18 is a partial cross section showing another modification ofthe optical disk shown in FIG. 1; and

[0029]FIG. 19 is a partial cross section showing another modification ofthe optical disk shown in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] Embodiments of the present invention will be describedhereinafter. FIG. 1 is a partial cross section (the thickness of eachlayer differs from that of an actual layer, and a guide groove isomitted from the drawing) showing an optical disk according to theembodiment of present invention. The embodiment shows an example inwhich the present invention is applied to a CD-R disk. As to opticaldisk 10, a pigment layer (i.e., a recording layer) 14, a reflectionlayer 16, a visible light characteristic changing layer 18 and aprotective layer 20 are sequentially formed on a single side of atransparent substrate so as to constitute the optical disk 10. Theoptical disk 10 is identical with an ordinary CD-R disk, except forprovision of the visible light characteristic changing layer 18. Thevisible light characteristic changing layer 18 can be seen through atransparent protective layer 20 from a label surface 22. Thereflectivity, permeability, or optical-scattering characteristic (i.e.,reflectivity, permeability, and spectrum light scattering) in an area ofthe visible light characteristic changing layer 18 is changed when thearea of the layer 18 is exposed to a laser beam having predeterminedpower or more from the label surface 22 side. The visible lightcharacteristic changing layer 18 can be formed from a material layer(i.e., a color changing layer, a photosensitive layer, or a heatsensitive layer) which changes in color, such as a photo-sensitivematerial or heat-sensitive material, e.g., change from white to color(e.g., black) or from transparent to color (e.g., black). When thevisible light characteristic changing layer 18 is formed from aphotosensitive layer, there can be employed photosensitive materialwhich is not photosensitized by the laser having power of less than 1mW, but is photosensitized to discolor the photosensitive layer by alaser beam of 780 nm having power of 1 mW or more, with respect to alaser beam of 780 nm from the laser surface 22 side. When the visiblelight characteristic changing layer 18 is formed from a heat-sensitivelayer, there can be employed heat sensitive material which is notsensitive to a heat of less than 100° C. but becomes sensitive to heatof 100° C. or higher to discolor the heat sensitive material. Further,the color-changing layer may be provided as the visible lightcharacteristic changing layers. The color-changing layer is formed fromtwo layers which are fused or mixed together by being exposed to thelaser beam, thereby changing a visible-light characteristic. Since thelaser beam for recording and playing the back data of the optical disk10 is entered from the substrate 12 side and so that the laser beam issubstantially cut off by the reflection layer 16. Therefore, the visiblelight characteristic changing layer 18 does not cause any change in thevisible-light characteristic of the laser beam.

[0031] As shown in FIG. 2, an intermediate layer 24 can be providedbetween the reflection layer 16 and the visible light characteristicchanging layer 18. The intermediate layer 24 can improve adhesionbetween a reflection layer and a visible light characteristic changinglayer, control heat conductivity contributing to changes in acharacteristic of visible light, and control heat insulating property toprotect data recorded on a recording surface of an optical disk. Thereflection layer and the intermediate layer can be joined directlytogether, and the intermediate layer and the visible lightcharacteristic changing layer can be joined directly together. As shownin FIG. 3, in place of the intermediate layer 24, the visible lightcharacteristic changing layer 18 is formed into a structure having aplurality of minute dots (e.g., each assuming a circular shape having adiameter of tens of micrometers or a non-circular shape of similarsize), through use of, e.g., a film transfer technique. Alternatively,in place of a plurality of minute pores, the visible lightcharacteristic changing layer 18 can be formed into a porous structurehaving a plurality of minute pores 26. In a case where the visible lightcharacteristic changing layer 18 is formed into the structure havingdots such as shown in FIG. 3, the reflection layer 16 and the protectivelayer 20 are joined together directly outside the dots. In a case wherethe visible light characteristic changing layer 18 is formed into thestructure having pores such as that shown in FIG. 4, the reflectionlayer 16 and the protective layer 20 are directly joined together withinthe pores. As a result, there can be achieved good adhesion, and heatinsulation control can be performed for the purpose of attaining theobject. Even when the visible light characteristic changing layer 18 istranslucence, the reflection layer 16 can be partially seen from thepart of the label surface 22, through an area where no visible lightcharacteristic changing layer 18 is present and at which the reflectionlayer 16 and the protective layer 20 are joined together directly. Atthe time of printing of the label surface 22, focusing on the reflectionlayer 16 can be achieved readily. The visible light characteristicchanging layer 18 can be made into a structure having concentric fringesor linear stripes.

[0032] As shown in FIG. 19, a light scattering layer 24 (a translucenceintermediate layer) may be provided between the visible lightcharacteristic changing layer 18 and the reflection layer 16. Byproviding the translucence intermediate layer 24, light, which passesthrough the visible light characteristic changing layer 18 and isreflected by the reflection layer 16, is not directly emitted from thesurface of the optical disk. That is, the light, which passes throughthe visible light characteristic changing layer 18, is scattered by thetranslucence intermediate layer 24. Therefore, light from the opticaldisk can be controlled by adjusting the translucence intermediate layer24, so that the various type of images can be formed on the surface ofthe optical disk as label.

[0033]FIG. 5 is a partial cross section (the thickness of each layerdiffers from that of an actual layer, and a guide groove is omitted fromthe drawing) showing another embodiment of the optical disk according tothe present invention. This embodiment is an example in which thepresent invention is applied to a CD-RW disk. As to an optical disk 28,a dielectric layer 32, a recording layer 34, a dielectric layer 36, areflection layer 38, a visible light characteristic changing layer 40,and a protective layer 42 are sequentially formed on a single of atransparent substrate 30 made of, for example, polycarbonate so as toconstitute the optical disk 28. The optical disk 28 is identical with anordinary CD-RW disk, except for provision of the visible lightcharacteristic changing layer 40. The visible light characteristicchanging layer 40 can be seen from a label surface 44 side through atransparent protective layer 42. The visible light characteristicchanging layer 40 can be constituted in the same manner as in thevisible light characteristic changing layer 18 shown in FIG. 1. As inthe case of the optical disk 10 shown in FIG. 2, an intermediate layercan be interposed between the reflection layer 38 and the protectivelayer 42 for the purpose set forth. Further, the visible lightcharacteristic changing layer 40 can be formed into a structure having aplurality of minute spots, as in the visible light characteristicchanging layer 18 shown in FIG. 3. Alternatively, the visible lightcharacteristic changing layer 40 can be formed into a porous structurehaving a plurality of minute pores, as shown in FIG. 4. As anotheralternative, the visible light characteristic changing layer 40 can beformed into a structure having concentric fringes or a structure havinglinear stripes.

[0034]FIG. 17 shows a partial cross section (the thickness of each layerdiffers from that of an actual layers, and a guide groove is omittedfrom the drawing) showing another embodiment of the optical diskaccording to the present invention. In this embodiment, a reflectionlayer for data recording and a reflection layer for imaging a label areseparately provided in the optical disk. That is, a second reflectionlayer 35 is formed between an intermediate layer 35 and a buffer layer37 (separation layer) as shown in FIG. 17. The second reflection layer35 is made of metal or derivative reflection material. Remain portion ofthe optical disk shown in FIG. 17 is identical to the optical disk shownin FIG. 5. In this embodiment, since the reflection layers 35 and 38 areseparately provided in the optical disk, mutual influence of recordingdata and printing label to the visible light characteristic changinglayer 40 and the recording layer 34 is reduced. Therefore, the influenceon formation of an image on the label surface is certainly eliminated.

[0035]FIG. 18 shows a partial cross section (thickness of each layerdiffers from that of an actual layers, and a guide groove is omittedfrom the drawing) showing another embodiment of the optical diskaccording to the present invention. This embodiment is an example inwhich the present invention is applied to an optical disk comprising twosubstrates adhered with other, such as a DVD (Digital video Disk). Theoptical disk in this embodiment is constituted as follows: a dielectriclayer 32, a recording layer 34, a dielectric layer 36 and a firstreflection layer 38 are sequentially formed on a first transparentsubstrate; a second reflection layer 35 made of metal or derivativereflection material, a translucence intermediate layer 39 (a lightscattering layer), a visible light characteristic changing layer 40 anda protective layer 42 are sequentially formed on a second substrate 33;and the second substrate 33 is built on the first substrate 30 through alaminating adhesive layer 31 as shown in FIG. 18. In case of DVD, eachsubstrate has a thickness of 0.6 mm and is laminated each other, so thatsum of thickness including a recording layer is 1.2 mm.

[0036]FIG. 6 shows an embodiment of the optical disk unit according tothe present invention (showing only the portions of the unit pertainingto printing of a label surface). The optical disk unit is configured asa CD-R/RW drive (an optical disk drive which enables recording andreproduction of data on and from a CD-R disk and a CD-RW disk) used withconnection with a host computer 46, such as a personal computer. Anoptical disk 50 according to the present invention (the CD-R disk shownin FIGS. 1 through 4 or the CD-RW disk 28 shown in FIG. 5, etc.) isplaced on a turn-table 54 while being inverted (i e., a label surface 52is turned down) and the optical disk 50 is driven to be rotated. Afrequency generator (FG) 58 is directly connected to a rotary shaft of aspindle motor 56. The frequency operation. At the time of printing alabel, the focus servo circuit 76 is turned on. At the time of recordingor reproduction of data, a tracking servo circuit 78 actuates a trackingactuator of the optical pickup 66 on the basis of a tracking errorsignal in accordance with the instruction output from the system controlcircuit 62, thus executing tracking control operation. At the time ofprinting a label, the tracking servo circuit 78 is turned off. At thetime of printing a label, a vibration signal generation circuit 80generates a predetermined vibration signal in accordance with theinstruction output from the system control circuit 62, and supplies thevibration signal to the tracking actuator. Accordingly, an object lensof the optical pickup 66 is vibrated in the radial direction of theoptical disk 50 to thereby bridge a gap between the areas circularlyscanned by a laser beam, as a result of which there is obtained a printproduct having no gaps.

[0037] The laser driver 82 drives a laser diode of the optical pickup 66to emit a laser beam onto the optical disk 50 in accordance with theinstruction output from the system control circuit 62, thereby executingrecording/reproduction of data or printing a label. At the time ofrecording of data, the laser diode outputs a laser beam of recordingpower modulated by a recording signal. At the time of reproduction ofdata, the laser diode outputs a laser beam of fixed reproduction power.At the time of printing label, the laser diode outputs a laser generator58 generates a pulse signal (FG pulse) for each turning angle, theturning angle being determined by dividing one rotation of the spindlemotor 56 by a predetermined integer. The FG pulse signal is multipliedby a predetermined number by a multiplier 60 constituted by a PLLcircuit. The thus-multiplied FG pulse is input to a system controlcircuit (CPU) 62, where the signal is used for detecting a peripheralposition. At the time of printing of a label surface, a spindle servocircuit 64 controls, on the basis of the FG pulse signal, the spindlemotor 56 so as to rotate constantly at a rotating speed instructed bythe system control circuit 62.

[0038] An optical pickup 66 is provided at a position under the opticaldisk 50 for executing recording and reproduction of data and printing ofa label. The optical pickup 66 is supported by a feed screw 68 so as tobe able to move in the radial direction of the optical disk 50. A feedmotor 72 is driven by a motor driver 70 in accordance with aninstruction output from the system control circuit 62 so as to rotatethe feed screw 68 so that the optical pickup 66 is moved in the radialdirection of the optical disk 50. A feed position sensor 74, such as alinear scale, detects the radial position of the optical pickup 66 onthe optical disk 50. In accordance with an instruction output from thesystem control circuit 62, a focus servo circuit 76 actuates a focusactuator of the optical pickup 66 on the basis of a focus error signal,thus executing focus control beam modulated based on image datapertaining to characters or graphic images to be printed (i.e., a laserbeam has high power so as to cause changes in the visible lightcharacteristic changing layer in an area to be printed and a laser beamhas low power so as not to cause changes in the visible lightcharacteristic changing layer in an area not to be printed). At the timeof printing a label, the host computer 46 transmits, to a CD-R/RW drive48, image data, which edited by a user and to be printed, pertaining tocharacters or graphic images. The image data is constituted by data(e.g., data which specify a print segment represented by an angle θ foreach radial position “r” at a predetermined pitch Δr) represented bycoordinates (r, θ), the coordinates corresponding to a combination of aradial position “r” of an optical disk (a distance from a rotationcenter) and a circumferential position θ (a circumferential anglerelative to an appropriate reference position).

[0039] Process of printing data on a label surface of the optical disk50 by the CD-R/RW drive 48 shown in FIG. 6 is performed in the mannerdescribed below.

[0040] (1) The optical disk 50 is set on the turntable 54 while beinginverted in case of recording data or reproducing, i.e. the optical disk50 is set so as to face the surface of the optical disk 50, which thelabel is to be printed, to the optical pick up 66.

[0041] (2) A user edits, on a display of the host computer 46,characters or a graphic image such as a picture to be printed. The hostcomputer 46 converts the thus-edited image into image data.

[0042] (3) The user instructs to start printing operation on the hostcomputer 46.

[0043] (4) The spindle servo circuit 64 subjects the spindle motor 56 toCAV (constant rotating speed) control so that the pulse generated by thefrequency generator 58 is to be a fixed frequency instructed by thesystem control circuit 62.

[0044] (5) The optical pickup 66 is positioned at a predetermined radialreference position at the inner radius of the optical disk 50.

[0045] (6) The laser driver 82 drives the laser diode so that the laserpower of a laser diode of the optical pickup 66 is to be a predeterminedlow output instructed by the system control circuit 62 (a value of whichenables focus control operation without involvement of occurrence ofchanges in the visible light characteristic changing layer; e.g., avalue of 1 mW or less).

[0046] (7) The focus servo circuit 76 is turned on in accordance withthe instruction output from the system control circuit 62. Then, thefocus servo circuit 76 executes focus servo operation so that the laserbeam 67 forms the minimum spot on the reflection layer. Here, thetracking servo circuit 78 remains off, and no tracking servo operationis performed.

[0047] (8) Through the foregoing operations, preparation for printing ismade, and printing is commenced in accordance with the instructionoutput from the system control circuit 62. That is, the system controlcircuit 62 receives image data from the host computer 46, then, drivesthe feed motor 72 to position the optical pickup 66 in a radial positionat the inner radius of the optical disk 50, where a first print locationis present. While appropriate timing based on the FG pulse signal (or adetection timing for a sensor additionally provided for detecting areference circumferential position) is taken as a circumferentialreference position, a circumferential position θ is detected by countinga pulse signal output from the multiplier 60 is counted. With respect tothe radial position on the disk, laser power is switched to apredetermined high output (a value at which changes arise in the visiblelight characteristic changing layer; for example, a value of 1 mW ormore) in each circumferential print position instructed on the basis ofimage data. As a result, changes (i.e., discoloration) arise in thereflection characteristic changing layer at the location exposed to thelaser beam of high output power, thereby performing printing operation.When the optical disk 50 returns to the circumferential referenceposition after having effected one rotation, the feed motor 62 inactuated so as to move the optical pickup 66 toward an outercircumference at a predetermined pitch Δr, and then, with respect to theradial position on the disk, laser power is switched to a predeterminedhigh output in each circumferential print position instructed on thebasis of image data. This printing operation is repeated to print sothat the optical pickup 66 is sequentially moved toward the outercircumference at the predetermined pitch Δr every one rotation. FIG. 7shows the locus of movement of the laser beam over the label surface 52of the optical disk 50 through the printing operation. In the areadesignated with thick lines, the laser power of the laser beam isswitched to high power, thereby performing printing operation. FIG. 8shows variations in the laser power of the laser beam when the printingoperation shown in FIG. 7 is performed.

[0048] Scanning is not performed at radial positions where there is noprint area, and, the optical pickup 66 moves to a radial position wherethe next print area is present by passing through the radial positionhaving no print area, and printing is performed. If the pitch Δr islarge, an image which is originally to be printed without interruptionin the radial direction is printed with gaps, as shown in FIG. 9. Incontrast, if the pitch Δr is made small, gaps can be made unnoticeable.However, the number of rotations required for printing data on theentire label surface is increased, and printing involves consumption oftime. For this reason, the CD-R/RW drive 48 drives a tracking actuatorwith a vibration signal (e.g., a sinusoidal signal or triangular signal)generated by the vibration signal generation circuit 80 during aprinting operation, thereby vibrating the objective lens in the radialdirection of the optical disk 50. As shown in FIG. 10, the laser beam isvibrated in the radial direction of the optical disk 50, therebyenabling a printing operation without gaps (or with occurrence of smallgaps) even at a comparatively large pitch Δr. The frequency of thevibration signal can be set to, e.g., several kilohertz or thereabouts.Further, the pitch Δr can be set to, e.g., 50 to 100 μm or thereabouts.

[0049]FIG. 11A shows a practical example of a print made on the labelsurface 52 by the CD-R/RW drive 48. FIG. 11B shows a partial enlargedview showing the locus of movement of a laser beam used during printingof the print example. The drawing shows that, when scanning in a radialposition r1 is performed, the laser power of the laser beam is increasedwithin an angular segment from θ1 to θ2. FIGS. 12A through 12C showother examples of print products made on the label surface 52 by theCD-R/RW drive 48. Arbitrary character information, such as disk titles,music titles, the names of artists, or pictures can be printed.

[0050]FIG. 13 shows another embodiment of the optical disk unitaccording to the present invention (showing only the elementscontributing to printing of a label surface). In a CD-R/RW drive 84, theoptical disk 50 (the CD-R disk 10 shown in FIG. 10 or the CD-RW disk 28shown in FIG. 5) according to the present invention is set on aturntable 86 while being inverted (i.e., while the label surface 52 isturned down). At the time of printing operation, the spindle motor 88 isnot driven. An optical pickup 90 for performing recording orreproduction of data is provided at a location under the optical disk50. The optical pickup 90 is supported by a feed screw 92 so as to bemovable in the radial direction of the optical disk 50. In accordancewith the instruction output from the system control circuit 62, a feedmotor 94 is driven by a motor driver 96, thereby rotating the feed screw92 so that the optical pickup 90 is moved in the radial direction of theoptical disk 50. The radial direction position of the optical pickup 90on the optical disk 50 is detected by a feed position sensor 98 such asa linear scale.

[0051] The entirety of the disk radial feed mechanism having the feedscrew 92 and the feed motor 94 is movably supported by a feed screw 101disposed in parallel with the plane of the disk 50 perpendicular to thefeed screw 92, so as to be movable in the direction tangent to a track(i.e., a direction perpendicular to a feed direction in the radialdirection of the disk). In accordance with an instruction output from asystem control circuit 105, a feed motor 103 is driven by a motor driver107 so as to rotate the feed screw 101. As a result, the optical pickup90 is moved in the direction tangent to a track. The position of theoptical pickup 90 in the direction tangent to a track is detected by afeed position sensor 109 such as a linear scale.

[0052]FIGS. 14A and 14B show a layout of a feed mechanism (neither afeed motor nor a feed screw is shown) as example. Slide bars 111 areprovided in and fixed to a mechanical base of the CD-R/RW drive 84 inparallel with the plane of the optical disk 50. An optical pickup unit113 is slidably supported on the slide bar 111. The optical pickup unit113 is moved along the slide bars 111 by the feed motor 103 and the feedscrew 101 (shown in FIG. 13). Slide bars 115 are mounted on and fixed tothe optical pickup unit 113 in parallel with the plane of the opticaldisk 50 and perpendicular to the slide bars 111. The optical pickup 90is slidably supported by the slide bars 115 and is moved along the slidebars 115 by the feed motor 94 and the feed screw 92 (shown in FIG. 13).At the time of printing operation, feed mechanisms feeding in twodirections are driven. At the time of recording/reproduction of data,only the mechanism feeding operation in the radial direction of a track(simply a “track-radial-direction feed mechanism”) is driven, and themechanism feeding in the direction tangent to a track (simply a“track-tangential-direction feed mechanism”) is stopped in a neutralposition thereof (i.e., the position in which an objective lens 90 a ofthe optical pickup 90 is moved in the radial direction of a disk bydriving the track-radial-direction feed mechanism).

[0053] The track-tangential-direction feed mechanism can move thespindle motor 88 instead of moving the optical pickup 90. In this case,a feed screw 117 and a feed motor 119 for moving the spindle motor 88 inthe same direction are provided in place of the feed screw 101 and thefeed motor 103 for moving the optical pickup 90 in the direction tangentto a track. FIGS. 15A and 15B show a layout of the feed mechanism insuch a case (neither the feed motor 119 nor the feed screw 117 is shown)as an example. Slide bars 121 are provided in and fixed to a mechanicalbase of the CD-R/RW drive 84 in parallel with the plane of the opticaldisk 50. A spindle motor 88 is slidably supported by the slide bars 121.The spindle motor 88 is moved along the slide bars 121 by a feed motor119 and a feed screw 117 (see FIG. 13). Slide bars 123 are mounted onand fixed to a mechanical base of the CD-R/RW drive 84. The opticalpickup 90 is slidably supported by the slide bars 123 and is moved alongthe slide bars 123 by the feed motor 94 and the feed screw 92 (shown inFIG. 13). At the time of printing operation, feed mechanisms feeding intwo directions are driven. At the time of recording/reproduction ofdata, only the track-radial-direction feed mechanism is driven. Thetrack-tangential-direction feed mechanism is stopped in a neutralposition thereof (i.e., the position in which an objective lens 90 a ofthe optical pickup 90 is moved in the radial direction of a disk bydriving the track-radial-direction feed mechanism).

[0054] In FIG. 13, in accordance with an instruction output from thesystem control circuit 105, a focus servo circuit 125 actuates a focusactuator of the optical pickup 90 on the basis of a focus error signal,thus performing focus control operation. At the time of printing alabel, the focus servo circuit 125 is turned on. At the time ofrecording or reproduction of data, a tracking servo circuit 127 actuatesa tracking actuator of the optical pickup 90 on the basis of a trackingerror signal in accordance with the instruction output from the systemcontrol circuit 105, thus performing tracking control operation. At thetime of printing a label, the tracking servo circuit 127 is turned off.At the time of printing a label, the vibration signal generation circuit129 generates a predetermined vibration signal in accordance with theinstruction output from the system control circuit 105, and supplies thevibration signal to the tracking actuator. Accordingly, an object lensof the optical pickup 90 is vibrated in the radial direction of theoptical disk to bridge a gap between the areas circularly scanned by alaser beam, as a result of which there is obtained a print producthaving no gaps.

[0055] In accordance with the instruction output from the system controlcircuit 105, a laser driver 131 drives a laser diode of the opticalpickup 66 to emit a laser beam onto the optical disk 50, therebyperforming recording/reproduction of data or printing of a labelsurface. At the time of recording of data, the laser diode outputs alaser beam of recording power modulated by a recording signal, bydriving action of the laser driver 131. At the time of reproduction ofdata, the laser diode outputs a laser beam whose recording power has afixed predetermined reproducing power. At the time of printing label,the laser diode outputs a laser beam modulated with image datapertaining to characters or graphic images to be printed (i.e., a laserbeam has high power to cause changes in the visible light characteristicchanging layer in an area to be printed and a laser has low power so asnot to cause changes in the visible light characteristic changing layerin an area not to be printed). At the time of printing a label, a hostcomputer 133 transmits, to the CD-R/RW drive 84, image data pertainingto characters or graphic images to be edited by the user and to beprinted. The image data are constituted by dot-matrix data (e.g., datawhich specify a print segment in the direction tangent to a trackrepresented by “t,” for each radial position “r” at a predeterminedpitch Δr) represented by coordinates (r, t), the coordinatescorresponding to a combination of a radial position “r” of an opticaldisk, which is a distance from an appropriate reference position (e.g.,rotation center) in the radial direction of the disk, and a position “t”in the direction tangent to a track, which is a distance from theappropriate reference position in the direction tangent to a track.

[0056] Process of printing data on a label surface of the optical disk50 by the CD-R/RW drive 84 shown in FIG. 13 is performed in the mannerdescribed below.

[0057] (1) The optical disk 50 is set on the turntable 86 while beinginverted in case of recording data or reproducing, i.e. the optical disk50 is set so as to face the surface of the optical disk 50, which thelabel is to be printed, to the optical pick up 90.

[0058] (2) A user edits, on a display of the host computer 133,characters or a graphic image such as a picture to be printed. The hostcomputer 133 converts the thus-edited image into image data.

[0059] (3) The user instructs to start printing operation on the hostcomputer 133.

[0060] (4) The spindle motor 88 is stopped in accordance with theinstruction output from the system control circuit 105 during the courseof printing operation.

[0061] (5) The optical pickup 90 is positioned in a predeterminedreference position.

[0062] (6) The laser driver 131 drives the laser diode so that laserpower of the laser diode of the optical pickup 90 is to be apredetermined low output instructed by the system control circuit 105(i.e., a value at which no changes arise in the visible lightcharacteristic changing layer and focus control operation can beeffected; for example, a value of 1 mW or less).

[0063] (7) In accordance with the instruction output from the systemcontrol circuit 105, the focus servo circuit 125 is turned on. As aresult, the focus servo circuit 125 performs focus servo operation sothat the laser beam forms the minimum spot on the reflection layer.Here, the tracking servo circuit 127 remains off, and no tracking servooperation is effected.

[0064] (8) Through the foregoing operations, preparation for printing ismade, and printing is commenced in accordance with the instructionoutput from the system control circuit 105. That is, the system controlcircuit 105 receives image data from the host computer 133 to drive thefeed motor 94 to position the optical pickup 90 in a radial position atthe inner radius of the optical disk 50, where a first print location ispresent. The motor 103 (or 119) is driven at the radial position, tomove a laser beam to the direction tangent to a track. In connectionwith the radial position on the disk, laser power is switched to apredetermined high output (a value at which changes arise in the visiblelight characteristic changing layer: for example, a value of 1 mW ormore) over a print segment in the direction tangent to a trackinstructed on the basis of image data. As a result, changes (i.e.,discoloration) arise in the reflection characteristic changing layer atthe location exposed to the laser beam of high output power, therebyperforming the printing operation. Then, the feed motor 94 is driven tomove the optical pickup 90 toward an outer circumference at apredetermined pitch Δr, and then with respect to this radial position onthe disk, the laser power is switched to a predetermined high outputlevel over the print segment in the direction tangent to a trackinstructed on the basis of the image data while the optical pickup 90 ismoved in that position in the direction tangent to a track, therebyperforming printing operation. This printing operation sequentiallyrepeated so that the optical pickup 90 is moved toward the outercircumference at the predetermined pitch Δr. FIG. 16 shows the locus ofmovement of the laser beam over the label surface 52 of the optical disk50 through the printing operation and a resultant print product. Thelaser beam is moved while being vibrated by the vibration signal, thereis produced a print product having no gaps (or having small gaps).

[0065] In the present embodiment, the visible light characteristicchanging layer is interposed between a reflection layer and a protectivelayer. However, the optical disk according to the present invention isnot limited to such a structure. The visible light characteristicchanging layer can be provided in any area (e.g., on a protective layer)viewed from a part of a label surface of an optical disk. Although theembodiment has described a case where the optical disk according to thepresent invention having a visible light characteristic changing layerformed integrally is subjected to printing, printing required by thelabel surface printing method and optical disk unit according to thepresent invention is not limited to such printing. More specifically, anoptical disk to which a label having a visible light characteristicchanging layer is affixed can be subjected to printing by application ofthe label surface printing method and optical disk unit according to thepresent invention. In the embodiment, a label surface is subjected toprinting while focus servo operation is being performed. However, whenno request exists for a print resolution, printing can be performedwithout involvement of focus servo operation. In that case, reflectedlight required for effecting focus servo operation is not necessary.Hence, the visible light characteristic changing layer can be formedinto a translucence form so as not to be able to see reflection layerthrough the visible light characteristic changing layer. In theembodiment, printing is performed by using modulating power of the laserbeam in accordance with image data. However, if there are parametersother than power which enable occurrence of changes in the visible lightcharacteristic changing layer by using modulating power in accordancewith image data, printing can be performed by modulating the parameters.The embodiment has described a case where changes arising in the visiblelight characteristic changing layer correspond to discoloration.However, the present invention is not limited to this embodiment. Anytype of change may be employed, so long as the change is visuallyrecognizable. In the embodiment, an optical disk is sequentiallysubjected to printing from its internal circumference to outercircumference. However, the present invention is not limited to such asequence. An optical disk may be sequentially subjected to printing fromits outer to inner circumference, or in another appropriate sequence.The embodiment has described a case where a CD-R disk or CD-RW disk issubjected to printing. However, the present invention can also beapplied to a case where another type of optical disk is subjected toprinting. Moreover, the embodiment has described a case where thepresent invention has been applied to the optical disk unit which isused while being connected to a host computer. However, the presentinvention can be also applied to an optical disk unit which is used in astandalone manner, such as a CD recorder.

What is claimed is
 1. A method of forming an image on a label surface ofan optical disk, the method comprising the steps of: forming a visiblelight characteristic changing layer in a position which can be viewedfrom a label surface side of an optical disk, the visible lightcharacteristic changing layer changing a characteristic of visible lightfrom the label surface by exposure to a laser beam, from the labelsurface side, used for recording a signal; setting the optical disk on aturntable of an optical disk unit so that a label surface of the opticaldisk is oriented toward a direction in which a laser beam from anoptical pickup is to enter; relatively moving the optical disk and thelaser beam along a plane of the optical disk; modulating the laser beam,in synchronism with the relative movement, into a specificcharacteristic in accordance with image data to be printed; and emittingthe modulated laser beam to the visible light characteristic changinglayer from the label surface side, wherein a reflection characteristicof the visible light in the visible light characteristic changing layeris changed by exposure, so that a image corresponding to the image datais printed on the label surface.
 2. The method according to claim 1,wherein the laser beam used for recording a signal is a laser beam ofpredetermined power or higher.
 3. The method according to claim 1,wherein the optical pickup is moved in a radial direction of the opticaldisk while the optical disk is being rotated.
 4. The method according toclaim 1, wherein the optical disk is made stationary, and the opticalpickup is moved in a radial direction of the optical disk and in adirection which is orthogonal to the radial direction of the opticaldisk and is tangent to a track.
 5. An optical disk unit comprising: arelative movement mechanism for relatively moving an optical disk set ona turntable in a state that a label surface is oriented in a directionin which a laser beam is to enter, and a laser beam emitted from anoptical pickup along a plane of the optical disk; a laser modulationcircuit for modulating a laser beam emitted from the optical pickup; anda controlling circuit for controlling the relative movement mechanismand the laser modulation circuit, wherein the control circuit controlsthe relative movement mechanism to relatively move the optical disk andthe laser beam, and controls the laser modulation circuit in accordancewith image data to be formed on a label surface of the optical disk sothat the laser beam emitted from the optical pickup on the basis of theimage data is modulated, an image corresponding to the image data isformed on an area which can be viewed from label surface side of theoptical disk.
 6. The optical disk unit according to claim 5, wherein therelative movement mechanism includes a rotary drive device forrotationally driving a turntable and a radial-direction feed drivedevice for moving the optical pickup in a radial direction of theoptical disk, and the control circuit controls the rotary drive deviceand the radial-direction feed drive device, for controlling relativemovement between the optical disk and the laser beam.
 7. The opticaldisk unit according to claim 6, wherein the control circuit drives therotary drive device to a constant rotating speed, for driving theradial-direction feed drive device by a predetermined amount at eachpredetermined rotary position.
 8. The optical disk unit according toclaim 6, further comprising: a circumferential-direction position sensorfor detecting a circumferential position of the optical disk, and aradial-direction position sensor for detecting a radial position of theoptical pickup on the optical disk, wherein the control circuitmodulates a laser beam emitted from the optical pickup in accordancewith the position detected by the circumferential-direction positionsensor and the radial-direction position sensor and the image data to beformed on a label surface of the optical disk.
 9. The optical disk unitaccording to claim 8, wherein the circumferential-direction positionsensor includes a frequency generator generates a signal of frequencycorresponding to rotation of the circumferential-direction positionsensor rotated by the rotary drive device, and a multiplier formultiplying the frequency of the signal generated by the frequencygenerator.
 10. The optical disk unit according to claim 5, wherein therelative movement mechanism includes a radial-direction feed drivedevice for moving the optical pickup in a radial direction of theoptical disk, and a track-tangential-direction feed drive device formoving the optical pickup in a direction which is perpendicular to theradial direction of movement and is tangent to a track of the opticaldisk; and the control circuit controls relative movement between theoptical disk and the laser beam by controlling the radial-directionposition sensor and the track-tangential-direction feed drive devicewhile the turntable is left in a stationary state.
 11. The optical diskunit according to claim 10, further comprising: acircumferential-direction position sensor for detecting acircumferential position of the optical disk; and atrack-tangential-direction position sensor for detecting a positionwhich is orthogonal to the radial direction of movement and is tangentto a track of the optical disk, wherein the laser beam emitted from theoptical pickup is controlled in accordance with the position detected bythe circumferential-direction position sensor and that detected by thetrack-tangential-direction position sensor, and image data to be formedon a label surface of the optical disk.
 12. The optical disk unitaccording to claim 5, wherein the control circuit controls relativemovement between the optical disk and the laser beam by turning off atracking servo and turning on a focus servo.
 13. The optical disk unitaccording to claim 5, wherein the control circuit performs a controloperation for vibrating and driving a tracking actuator of the opticalpickup while controlling relative movement between the optical disk andthe laser beam.
 14. An optical disk comprising: a visible lightcharacteristic changing layer which changes a visible characteristic ofa laser beam by exposure to a laser beam having entered from a labelsurface side and which is formed in a location capable of being viewedfrom the label surface side.
 15. The optical disk according to claim 14,wherein the visible light characteristic changing layer is acolor-changing layer which undergoes fading, coloring, or changes incolor or hue by exposure to the laser beam.
 16. The optical diskaccording to claim 15, wherein the color-changing layer is one of aphotosensitive or heat sensitive layer, and two layers fused or mixedtogether by exposure to the laser beam so as to change visible-lightcharacteristic.
 17. The optical disk according to claim 14, wherein theoptical disk is constituted by at least a recording layer, a firstreflection layer, the visible light characteristic changing layer and aprotective layer which are sequentially formed on a substrate.
 18. Theoptical disk according to claim 17, wherein an intermediate layer isdisposed between the first reflection layer and the visible lightcharacteristic changing layer; and the first reflection layer and theintermediate layer are joined directly together, and the intermediatelayer and the visible light characteristic changing layer are joineddirectly together.
 19. The optical disk according to claim 17, wherein apart containing the visible light characteristic changing layer and apart which does not include the visible light characteristic changinglayer and is joined directly to the first reflection layer and to theprotective layer are formed so as to be finely mixed between the firstreflection layer and the protective layer.
 20. The optical diskaccording to claim 19, wherein the visible light characteristic changinglayer is formed between the first reflection layer and the protectivelayer in the form of a plurality of dots or a plurality of voids, andthe first reflection layer is joined directly to the protective layer atoutsides of the plurality of dots or insides of the plurality of voids.21. The optical disk according to claim 14, wherein a light scatteringlayer, which is translucence and has a light scattering characteristic,is interposed between the first reflection layer and the visible lightcharacteristic changing layer.
 22. The optical disk according to claim21, wherein the light scattering layer serves as an intermediate layer.23. The optical disk according to claim 17, wherein the recording layeris provided substantially intermediate position between the labelsurface and a surface in which a laser beam for recording enters, thefirst reflection layer is provided to the recording layer, and thevisible light characteristic changing layer is provided on one of asecond reflection layer and a translucence light scattering layerseparated from the first reflection layer.
 24. A optical diskcomprising: a first substrate; a recording layer provided on thesubstrate; a first reflection layer provided on the recording layer; avisible light characteristic changing layer provided on the reflectionlayer, a visible light characteristic thereof being changed by exposureto a laser beam; and a protective layer
 25. The optical disk accordingto claim 24 further comprising an intermediate layer provided betweenthe first reflection layer and the visible light characteristic changinglayer.
 26. The optical disk according to claim 24 further comprising alight scattering layer provided between the first reflection layer andthe visible light characteristic changing layer.
 27. The optical diskaccording to claim 24 further comprising; a buffer layer provided on thefirst reflection layer; and a second reflection layer provided betweenthe buffer layer and the visible light characteristic changing layer.28. The optical disk according to claim 24 further comprising: a secondsubstrate provided on the first reflection layer; and a secondreflection layer provided on the second substrate.
 29. a method offorming an image on a optical disk which includes a substrate, arecording layer on the substrate, a reflection layer on the recordinglayer and a visible light characteristic changing layer on thereflection layer, by utilizing a laser beam, for recording a signal inthe recording layer, emitted from an optical pickup of an optical diskunit, the method comprising the steps of: setting the optical disk on aturntable of the optical disk unit so that the visible lightcharacteristic changing layer is oriented toward the optical pickup; andrelatively moving the optical disk and the optical pickup, modulatingthe laser beam and emitting the modulated laser beam to the visiblelight characteristic changing layer based on image data from a hostcomputer, so that the image corresponding to the image data is formed onthe optical disk.